1. Field of the Invention
The present invention relates to the production of nanoporous silica dielectric films and to semiconductor devices and integrated circuits comprising these improved films. The invention relates to nanoporous films having improved mechanical strength, i.e., modulus and hardness. More particular, the invention relates to the preparation of a soluble polymer precursor solution for spin coating.
2. Description of the Related Art
As feature sizes in integrated circuits are reduced to below 0.15 μm and below, problems with interconnect RC delay, power consumption and signal cross-talk have become increasingly difficult to resolve. It is believed that the integration of low dielectric constant materials for interlevel dielectric (ILD) and intermetal dielectric (IMD) applications will help to solve these problems. While there have been previous efforts to apply low dielectric constant materials to integrated circuits, there remains a longstanding need in the art for further improvements in processing methods and in the optimization of both the dielectric and mechanical properties of such materials used in the manufacture of integrated circuits.
It is important for conventional dielectrics to possess a low dielectric constant as low as possible, toward a theoretical limit of 1.0. The practical expectation for polymer dielectrics as bulk materials is a dielectric constant range of 2.3–3.0, along with easy processibility by standard spin-bake-cure processing techniques. The dielectrics should also be free from moisture adsorption and out-gassing problems, in addition to their expected adhesive qualities and their dimensional stability towards thermal cycling, etching, and CMP processes. Organic dielectrics should have Tg values as high as possible toward 500° C., a value determined by the thermal stability of organic polymers. The high temperature conditions for multilayer construction and thermal cycling demand that the Tg be >400° C. The demand for a dielectric constant lower than 2.3 necessitates the development of dielectric materials with designed-in nanoporosity, either with nano-sized voids with controlled formation, or molecular free volume to reduce the bulk density and refractive index. Voids in polymer film structures may result in a lowering of mechanical strength. Therefore, a “closed” pore structure with small pore size distribution as well as uniform pore distribution throughout the matrix is preferred. Formation of such a “closed” pore structure with a lowering of dielectric constant and improved mechanical strength is very attractive to the process of integration. It precludes the difficulty of developing new process integration schemes, and avoids expensive purchases of new tools and/or modification of existing tools. Another very desirable feature is the etch/wet clean selectivity with inorganic anti-reflective coatings (ARC) materials. It facilitates the process integration of a hybrid low k film with an inorganic film such as ARC in the development of integrated circuits. Also a desirable feature in these thin films is the tenability of film thickness from 1,000 A to 25,000 A. The film thickness for spin-on dielectric is controlled by spin speed, matrix solution molecular weight, and solution viscosity. The solution viscosity is a function of matrix molecular weight, solvent and solution concentration at a given temperature.
The present invention relates to hybrid inorganic/organic chemical compositions for use in forming low k dielectric materials. In existing inorganic low k dielectric materials, a certain amount of an organic moiety is essential in producing hydrophobic films with the desired dielectric properties. However, this is done at the expense of weakening the mechanical strength, i.e. modulus and hardness, because pending organic groups in the network would reduce the mechanical strength of the silica network.
A layer of the composition is coated onto a substrate, crosslinked to produce a gel film, and then heated at a temperature and for a duration effective to remove substantially all of the porogen to thereby produce a nanoporous silica dielectric film.
In using a pre-polymer of the above Formula 1, a decrease in mechanical strength caused by free organic groups is eliminated or reduced, while a certain amount of organic moiety is maintained. An increase in organic content in the inorganic/organic hybrid materials would also provide the desired dielectric properties, which is an essential factor to the success of inorganic low k dielectric materials.